Lumber drying kiln



Sept. 27, 1955 v. A. BLOXHAM LUMBER DRYING KILN Filed May 17, 1952 INVENTOR. Var/m A. B/oxham ATTORNEY United States Patent LUMBER DRYING KILN Verlin A. Bloxham, Berkeley, Calif. Application May 17, 1952, Serial No. 288,398-

6 Claims. (Cl. 34-223) This invention relates to the drying of lumber.

It is desirable to reduce the drying time of lumber over that provided by atmospheric or air-drying and to this end various kiln constructions and drying methods have been proposed. The present invention provides a. kiln construction and a method or process of drying enabling the moisture content of freshly cut lumber to be reduced to a desired value with an absence of checking, cracking or warping of the wood. In addition, the

drying is uniform throughout the charge or load in the drying kiln.

In accordance with the present invention, a fuel is burned directly in a combustion chamber and the products of combustion from the burning of the fuel, mixed with the air stream supplied to support combustion and with a portion of the atmosphere from the kiln, is circulated directly into the kiln, thus. enabling substantially all of the heat from combustion of the fuel to be applied directly to the drying of the lumber. This is attained without any hazard of burning the wood or kiln because of the dilution of the products of combustion. The only air added to the system is that utilized to support combustion of the fuel, thus enabling an adequately high relative humidity to be maintained within the kiln, an essential in the programing of the drying of the lumber. Within the kiln, the atmosphere is circulated at a velocity which is independent of the velocity of discharge of the gases from the combustion furnace, a step which enables the uniformity of drying to be attained.

It is in general the broad object of the present invention to provide a novel and an improved lumber kiln construction.

A further object of the present invention is to provide a novel method for the drying of lumber, particularly one utilizing a drying gas including products of.

combustion.

The invention includes other objects and features of advantage, some of which, together with the foregoing, will appear hereinafter wherein the present preferred form of apparatus and method. of operation of a lumber kiln are set forth.

In the drawings accompanying and. forming a part hereof, Figure 1 is a side elevation. partly in section, illustrating the construction of the kiln. t r

Figure 2 is a section taken along line 22 in Figure 1.

Figure 3 is a plan view of the upper distribution duct.

Referring to the drawings, the kiln includes a relatively elongated tunnel-like building, generally indicated at 6, and having vertical side-walls 7, a floor 8 and an arched roof 9 extending between the side-walls and over the load. In the kiln shown a pair of spaced tracks 11 are provided upon the floor to permit stacks of lumber, generally indicated at 12, to be moved into position as upon a flat bedded truck 13, the latter having suitable wheels 14. Doors (not shown) are provided at least at one end of the tunnel to permit the tunnel to be loaded and unloaded, the doors being closed to confine the load. A plurality of spaced stacks of lumber are usually provided in the kiln, depending upon the length thereof.

Extending centrally of the roof 9 is an upper distribution conduit generally indicated at 16, made up of a plurality of separate sections 17 each of which, as taken along the run of the conduit, are successively of narrower width so that the hot drying gas is released into the atmosphere on each 'side of the duct from the space between the adjacent ducts, as at 18. In addition, each duct section. includes an inner duct section 19 each of which in turn decreases in width along the run of the conveyor so that a substantial portion of the hot atmosphere is carried centrally along the distribution duct and only a portion thereof is released into an outer portion of the duct section 17 through the space indicated at 21. v

A return duct is provided along floor 8 and between the tracks 11, this duct being constructed in a manner similar to the distribution duct 16 except that the sevheat tunnel effects a uniform mixing of the products of combustion with the primary and secondary air" and with the return atmosphere from duct 22. The hot gas stream containing the products of combustion is discharged at a temperature of l00-200, a blower generally indicated at 27 being utilized for this purpose.

Baffles 31 are suspended by means not shown from" the roof and include movable end sections 32' which can be raised when the loads are being moved about iri the tunnel, and lowered into position when the loads are stationary to prevent short circuiting of the atmosphere and force it down through the loads, the baflies in this case engaging the top of the loads, as is shown in Figure 2.

Disposed at spaced intervals along the roof of the tunnel and coinciding substantially with the midpoint of each load of lumber, are a plurality of atmosphere circulating fans generally indicated at 33', and including a prime mover 34, a driven shaft 36, for a multi-blade fan 37.

In operation, the kiln being loaded and a stack of lumber being provided on each side of the kiln withits midpoint substantially coinciding withv thetransverse axis-of the kiln passing through a fan 33,. hot gas is supplied from the heater through the kiln. Simultaneously,

fans 33 are operated to circulate the atmosphere within the I have found that each fan should move the atmosphere within the kiln at a rate substantially twice that at which. the hot gases are supplied to the: kiln. In one operation wherein tenseparate stacks of lumber were provided, five along each side of the; kiln, the hot combustion gases were supplied at 180 F. and at the rate of six to seven thousand cubic feet per minute while each fan 33 circulated the atmosphere within the kiln at the rate of about 12,000 cubic feet per minute, providing a stack of velocity of 150-200 feet per minute. The air within the kiln was at a temperature of 200 F. The relative humidity was varied as desired and in accordance with the program settled on for the particular lumber undergoing drying, an operation well-known to those versed in the art. The lumber dried rapidly and yet did not check, crack or warp and each stack was uniformly dried, a feature of considerable importance.

From the foregoing, I believe it will be apparent that I have provided a novel, simple and improved lumber drying kiln and a novel and simple and improved method of drying lumber.

I claim:

1. In a lumber drying kiln of the character described for drying stacks of lumber, a tunnel having a floor, opposite sides and a roof; a hot air inlet conduit extending centrally along the roof of the tunnel for discharging hot air outwardly toward each of the opposite sides of the tunnel at a plurality of spaced points along the tunnel; a bafiie extending in a spaced relation to the roof and toward each side of the tunnel at an elevation above that of lumber stacked in the kiln, the baffle terminating in a spaced relation to each side of the tunnel to define a passageway with the roof of the tunnel for hot air discharged from said hot air conduit and to discharge air downwardly along each side of the tunnel; and a plurality of circular apertures in said baflle, each of said apertures being provided with a fan, the blades of which fan fit closely into said apertures to draw in the atmosphere of the tunnel and force such atmosphere to mix with hot air in said passageway for discharge therefrom onto lumber in the kiln.

2. In a kiln for drying lumber in stacks, a tunnel having a floor, opposite sides and a roof; a hot air inlet conduit extending along the roof of the tunnel for discharging hot air outwardly toward each of the opposite sides of the tunnel at a plurality of spaced points along the tunnel, means defining a passageway extending above lumber stacks in the tunnel for directing hot air discharged from said conduit outwardly toward each side of the tunnel; and a plurality of circular apertures in said means defining a passageway, each of said apertures being provided with a fan, the blades of which fit closely into said apertures, said fans being operable to draw the atmosphere of the tunnel into said passageway and force such atmosphere to mix with hot air in said passageway prior to discharge of hot air onto the lumber stacks.

3. In a kiln for drying lumber in stacks, a tunnel having a floor, opposite sides and a roof; a hot air inlet conduit extending along the roof of the tunnel for discharging hot air outwardly toward each of the opposite sides of the tunnel at a plurality of spaced points along the tunnel and at a first volume; means defining a passageway extending above lumber stacks in the tunnel and outwardly toward the sides of the tunnel for directing hot air discharged from said conduit outwardly toward each side of the tunnel; and a plurality of circular apertures in said means defining a passageway, each of said apertures being provided with a fan, the blades of which fit closely into said apertures, said fans being operable to draw the atmosphere of the tunnel into said passageway at a second volume substantially twice said first volume and force such atmosphere to mix with hot air in said passageway prior to discharge of hot air onto the lumber stacks.

4. In a lumber drying kiln of the character described for drying stacks of lumber, a tunnel having a floor, opposite sides and a roof; a hot air inlet conduit extending centrally along the roof of the tunnel for discharging hot air outwardly toward each of the opposite sides of the tunnel at a plurality of spaced points along the tunnel; a bafile extending in a spaced relation to the roof and toward each side of the tunnel at an elevation above that of lumber stacked in the kiln, the baflle terminating in a spaced relation to each side of the tunnel to define a passageway with the roof of the tunnel for hot air discharged from said hot air conduit and to discharge air downwardly along each side of the tunnel; a plurality of circular apertures in said bafiie, a fan mounted cooperatively in each of said apertures, each fan having blades fitting closely into an aperture to draw in the atmosphere of the tunnel and force such atmosphere to mix with hot air in said passageway for discharge therefrom onto lumber in the kiln, and an outlet conduit extending centrally along said floor and having an opening therein substantially directly beneath each of said fans.

5. In a kiln for drying lumber in stacks, a tunnel having a floor, opposite sides and a roof; a hot air inlet conduit extending along the roof of the tunnel for discharging hot air outwardly toward each of the opposite sides of the tunnel at a plurality of spaced points along the tunnel, means defining a passageway extending from lumber stacks in the tunnel for directing hot air discharged from said conduit outwardly toward each side of the tunnel; and a plurality of circular apertures in said means defining a pasageway, each of said apertures being provided between an adjacent pair of hot air outlets, a fan mounted cooperatively in each aperture with the blades fitting the aperture and operable to draw the atmosphere of the tunnel into said passageway and force such atmosphere to mix with hot air in said passageway prior to discharge of hot air onto the lumber stacks, and an air outlet conduit extending along the floor and having an inlet substantially direct below each fan.

6. In a kiln for drying lumber in stacks, a tunnel having a floor, opposite sides and a roof; a hot air inlet conduit extending along the roof of the tunnel for discharging hot air outwardly toward each of the opposite sides of the tunnel at a plurality of spaced points along the tunnel, means defining a passageway extending above lumber stacks in the tunnel for directing hot air discharged from said conduit outwardly toward each side of the tunnel; and a plurality of circular apertures in said means defining a passageway, each of said apertures being provided between an adjacent pair of hot air outlets, a fan mounted cooperatively in each aperture with its blades fitting the aperture and operable to draw the atmosphere of the tunnel into said passageway at a second volume substantially twice said first volume and force such atmosphere to mix with hot air in said passageway prior to discharge of hot air onto the lumber stacks, and an air outlet conduit extending along the floor and having an inlet substantially directly below each fan.

References Cited in the file of this patent UNITED STATES PATENTS 1,393,086 Carrier Oct. 11, 1921 2,251,617 Pirnie Aug. 5, 1941 2,439,011 Larkin et a1. Apr. 6, 1948 2,538,888 Smith Jan. 23, 1951 

